blob: 83079a09b72604cc2fcc7cd962b8a11d1543b423 [file] [log] [blame]
Matteo Scandoloa6a3aee2019-11-26 13:30:14 -07001// Copyright 2012 Google, Inc. All rights reserved.
2//
3// Use of this source code is governed by a BSD-style license
4// that can be found in the LICENSE file in the root of the source
5// tree.
6
7package layers
8
9import (
10 "encoding/binary"
11 "errors"
12 "github.com/google/gopacket"
13)
14
15// MPLS is the MPLS packet header.
16type MPLS struct {
17 BaseLayer
18 Label uint32
19 TrafficClass uint8
20 StackBottom bool
21 TTL uint8
22}
23
24// LayerType returns gopacket.LayerTypeMPLS.
25func (m *MPLS) LayerType() gopacket.LayerType { return LayerTypeMPLS }
26
27// ProtocolGuessingDecoder attempts to guess the protocol of the bytes it's
28// given, then decode the packet accordingly. Its algorithm for guessing is:
29// If the packet starts with byte 0x45-0x4F: IPv4
30// If the packet starts with byte 0x60-0x6F: IPv6
31// Otherwise: Error
32// See draft-hsmit-isis-aal5mux-00.txt for more detail on this approach.
33type ProtocolGuessingDecoder struct{}
34
35func (ProtocolGuessingDecoder) Decode(data []byte, p gopacket.PacketBuilder) error {
36 switch data[0] {
37 // 0x40 | header_len, where header_len is at least 5.
38 case 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f:
39 return decodeIPv4(data, p)
40 // IPv6 can start with any byte whose first 4 bits are 0x6.
41 case 0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f:
42 return decodeIPv6(data, p)
43 }
44 return errors.New("Unable to guess protocol of packet data")
45}
46
47// MPLSPayloadDecoder is the decoder used to data encapsulated by each MPLS
48// layer. MPLS contains no type information, so we have to explicitly decide
49// which decoder to use. This is initially set to ProtocolGuessingDecoder, our
50// simple attempt at guessing protocols based on the first few bytes of data
51// available to us. However, if you know that in your environment MPLS always
52// encapsulates a specific protocol, you may reset this.
53var MPLSPayloadDecoder gopacket.Decoder = ProtocolGuessingDecoder{}
54
55func decodeMPLS(data []byte, p gopacket.PacketBuilder) error {
56 decoded := binary.BigEndian.Uint32(data[:4])
57 mpls := &MPLS{
58 Label: decoded >> 12,
59 TrafficClass: uint8(decoded>>9) & 0x7,
60 StackBottom: decoded&0x100 != 0,
61 TTL: uint8(decoded),
62 BaseLayer: BaseLayer{data[:4], data[4:]},
63 }
64 p.AddLayer(mpls)
65 if mpls.StackBottom {
66 return p.NextDecoder(MPLSPayloadDecoder)
67 }
68 return p.NextDecoder(gopacket.DecodeFunc(decodeMPLS))
69}
70
71// SerializeTo writes the serialized form of this layer into the
72// SerializationBuffer, implementing gopacket.SerializableLayer.
73// See the docs for gopacket.SerializableLayer for more info.
74func (m *MPLS) SerializeTo(b gopacket.SerializeBuffer, opts gopacket.SerializeOptions) error {
75 bytes, err := b.PrependBytes(4)
76 if err != nil {
77 return err
78 }
79 encoded := m.Label << 12
80 encoded |= uint32(m.TrafficClass) << 9
81 encoded |= uint32(m.TTL)
82 if m.StackBottom {
83 encoded |= 0x100
84 }
85 binary.BigEndian.PutUint32(bytes, encoded)
86 return nil
87}